The present invention relates to an injection-molding apparatus for molding a multi-layered article and a method of injection-molding a multi-layered article.
In recent years, containers formed of thermoplastic resins are widely used as containers for cosmetics, foods, beverages and the like. The development of containers formed of a polyethylene terephthalate resin (to be sometimes abbreviated xe2x80x9cPET resinxe2x80x9d, hereinafter) in particular is rapidly advancing owing to improvements in biaxial orientation blow molding technology. However, a container formed of a biaxially oriented thermoplastic polyester resin composed mainly of PET resin does not necessarily have complete performances. That is, when the content to be filled in a container is a food which requires high gas barrier properties against oxygen gas and carbon dioxide gas, and therefore, the container formed of PET resin has a defect that the taste of the contents is impaired. With recent downsizing of containers, the containers are increasingly required to have higher gas barrier properties.
For satisfying the above requirement, JP-A-57-128520 (corresponding to U.S. Pat. No. 4,535,901) discloses a method in which an injection-molding apparatus having two injection cylinders for separately plasticizing and melting a thermoplastic polyester resin and an m-xylylene-group-containing polyamide resin (to be sometimes abbreviated as xe2x80x9cMX nylon resinxe2x80x9d, hereinafter) which is a thermoplastic gas-barrier resin, respectively, and having a single mold is used, and in one molding cycle, the molten thermoplastic polyester resin is injected, the molten MX nylon resin is injected while the molten thermoplastic polyester resin is being injected, and the injection of the molten thermoplastic polyester resin is continued even after completion of injection of the molten MX nylon resin, to form a parison having a three-layer structure of the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer. The above injection molding method is called a simultaneous-injection molding method.
Further, JP-A-60-240409 (corresponding to EP No. 161625/1985) discloses an injection-molding method similar to the above method, in which, for example, a molten thermoplastic polyester resin and a molten MX nylon resin are injected under specific conditions in the order of the molten thermoplastic resin, the molten MX nylon resin and the thermoplastic polyester resin, to form a parison having a five-layer structure of the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer. The above method is called an alternate-injection molding method.
In recent years, further, a technique is being developed for pelletizing collected containers composed mainly of PET resin and recycling them as a recycled PET resin. When the above recycled PET resin (including a PET resin reclaimed from defective products in the production of parisons and a recycled PET resin once used in the production of parisons) is used to produce parisons for beverage containers, it is required to form a parison having a three-layer structure of the PET resin layer/the recycled PET resin layer/the PET resin layer or a five-layer structure of the PET resin layer/the recycled PET resin layer/the PET resin layer/the recycled PET resin layer/the PET resin layer.
The methods disclosed in the above Japanese Laid-open Patent Publications have enabled the production of multi-layered containers (multi-layered bottles) having an appearance and mechanical performances equivalent to those of a container formed of a polyethylene terephthalate resin and having greatly improved barrier properties against oxygen gas and carbon dioxide gas, and thus-produced containers are now being used.
Conventionally, when a multi-layered molded article (e.g., a multi-layered parison as a precursor of a multi-layered container) formed of two or more resins is produced by virtue of two or more injection cylinders, there is used an injection molding apparatus having a mold provided with a cavity and having two or more injection cylinders. For example, in an injection molding apparatus having two injection cylinders, resin flow-passages (a first resin-flow-passage in which a first molten resin flows and a second resin-flow-passage in which a second molten resin flows) connecting the insides of the injection cylinders to the cavity are structured so as to meet with each other in a junction portion upstream of a gate portion opened to the cavity. Portions of the first and second resin-flow-passages positioned within the mold have a hot runner structure. Further, portions of the first and second resin-flow-passages upstream of the junction portion generally have the structure of a multiple tube. A screw provided in each injection cylinder is generally structured so as to move back when a pressure is exerted from the resin-flow-passage in any case other than the cases of injection of the molten resin and application of a dwell pressure, so that the molten resin in each resin-flow-passage flows back into each injection cylinder.
In the injection molding apparatus having the above structure, when a first molten resin for forming the outermost layer of the multi-layered article is injected into the cavity through the first resin-flow-passage for completely filling the cavity with the first and second molten resins, the first molten resin flowing in the first resin-flow-passage flows into the second resin flow-passage. In this case, the inflow of the first molten resin is not constant. As a result, the amount of the first molten resin to be injected into the cavity is destabilized. Further, during the first injection of the first molten resin, the second molten resin present in the second resin-flow-passage near the junction portion and the first molten resin are injected into the cavity together in a state of a mixture of these resins. There is therefore caused a problem that the second resin which is not to compose the outermost layer of the multi-layered article comes to exist on the outermost layer surface.
For preventing the above flow of the first molten resin into the second resin-flow-passage, a prior art uses a hydraulic shut-off valve provided in a nozzle portion of the injection cylinder which is for injecting second molten resin. Only during the injection of the second molten resin, the shut-off valve is opened, and in any other case, the shut-off valve is closed, whereby the flowing of the first molten resin into the second resin-flow-passage is prevented.
When the flow of a molten resin is controlled by means of the shut-off valve, the flowing of the first molten resin into the second resin-flow-passage can be prevented. However, there is caused the following problem. During the first injection of a first molten resin, the first molten resin and a second molten resin are mixed in the vicinity of the junction portion of the resin-flow-passages, or a second molten resin which is not in an injected state is taken into the first molten resin which is being injected. As a result, the second molten resin present near the junction portion flows into the cavity, and the second resin comes to exist on the surface of the multi-layered article. That is, there is caused a problem that the second resin which is not to compose the outermost layer of the multi-layered article comes to exist on the outermost layer surface.
JP-A-61-206612 (corresponding to U.S. Pat. No. 4,657,496) discloses a hot liner mold for injection-molding, which has a first resin-flow-passage 11 and a second resin-flow-passage 12, the second resin-flow-passage 12 being provided with a check valve 13. It is said that when a first resin material A is injected, a cavity 22 is completely filled with the resin but that since the second resin-flow-passage 12 is provided with the check valve 13, a second resin material B flows back due to the first resin material A in no case.
It is an object of the present invention to provide an injection molding apparatus for producing a multi-layered article which is formed of at least two resins and has resin layers of these resins laminated, and which is structured such that the resin which is not to compose the outermost layer of the multi-layered article can be reliably prevented from coming to exist on the outermost layer surface thereof, in other words, which is structured such that the resin which is not to compose the outermost layer of the multi-layered article is reliably sealed (blocked) with a resin layer composing the outermost layer of the multi-layered article, and a method of injection molding the above multi-layered article.
The above object is achieved by an injection molding apparatus for injection molding a multi-layered article, provided by the present invention, which comprises;
(a) a mold having a cavity block provided with a cavity and a hot runner block,
(b) at least a first injection cylinder and a second injection cylinder,
(c) a first resin-flow-passage for connecting an inside of the first injection cylinder and the cavity, and
(d) a second resin-flow-passage for connecting an inside of the second injection cylinder and the cavity,
the injection molding apparatus having a structure in which;
those portions of the first and second resin-flow-passages which are located within the mold are provided in the hot runner block, and
the first resin-flow-passage and the second resin-flow-passage meet with each other in a junction portion upstream of a gate portion opened to the cavity,
the injection molding apparatus being provided with a back flow device for letting first molten resin in the first resin-flow-passage flow into the second resin-flow-passage after second molten resin is injected into the cavity through the second resin-flow-passage,
the back flow device being operable in response to a pressure which the first molten resin in the first resin-flow-passage exerts on the second molten resin in the second resin-flow-passage.
In the present specification, the term xe2x80x9cupstreamxe2x80x9d means a position on the injection cylinder 30 side, xe2x80x9cdownstreamxe2x80x9d means a position on the cavity side, and these terms will be used in these senses hereinafter.
A method of injection molding a multi-layered article, according to a first aspect of the present invention for achieving the above object, is an alternate-injection molding method for which the above injection molding apparatus of the present invention is applied. That is, the method of injection molding a multi-layered article, according to the first aspect of the present invention for achieving the above object, is a method using an injection molding apparatus which comprises;
(a) a mold having a cavity block provided with a cavity and a hot runner block,
(b) at least a first injection cylinder and a second injection cylinder,
(c) a first resin-flow-passage for connecting an inside of the first injection cylinder and the cavity, and
(d) a second resin-flow-passage for connecting an inside of the second injection cylinder and the cavity,
the injection molding apparatus having a structure in which;
those portions of the first and second resin-flow-passages which are located within the mold are provided in the hot runner block, and
the first resin-flow-passage and the second resin-flow-passage meet with each other in a junction portion upstream of a gate portion opened to the cavity,
the injection molding apparatus being provided with a back flow device for letting first molten resin in the first resin-flow-passage flow into the second resin-flow-passage after second molten resin is injected into the cavity through the second-resin-flow-passage,
the back flow device being operable in response to a pressure which the first molten resin in the first-resin-flow-passage exerts on the second molten resin in the second resin-flow-passage,
the method comprising the steps of;
(A) injecting first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage and then discontinuing the injection of the first molten resin,
(B) injecting second molten resin prepared in the second injection cylinder into the cavity through the second resin-flow-passage and then terminating the injection of the second molten resin, and then,
(C) injecting first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage and letting first molten resin in the first resin-flow-passage flow into the second resin-flow-passage on the basis of operation of the back flow device during the injection of the first molten resin or after completion of injection of the first molten resin.
In the method of injection molding a multilayered article according to the first aspect of the present invention, although depending upon injection molding conditions, a main portion of the multilayered article may be formed to have a five-layer structure of the first resin layer/the second resin layer/the first resin layer/the second resin layer/the first resin layer. Otherwise, part of a main portion of the multi-layered article may be formed to have a five-layer structure of the first resin layer/the second resin layer/the first resin layer/the second resin layer/the first resin layer, and another part of the main portion of the multi-layered article may be formed to have a three-layer structure of the first resin layer/the second resin layer/the first resin layer. In these cases, a portion other than the main portion of multi-layered article is formed of a layer of the first resin.
FIGS. 14, 15 and 16 show changes of injection pressure, etc., with the lapse of time in the method of injection molding a multi-layered article according to the first aspect of the present invention. In FIGS. 14 to 21, xe2x80x9cclosed statexe2x80x9d in xe2x80x9cstate of back flow devicexe2x80x9d means that the inside of the second injection cylinder and the cavity are maintained in a non-communicated state on the basis of operation of the back flow device, and xe2x80x9copen statexe2x80x9d means that the inside of the second injection cylinder and the cavity are maintained in a communicated state by virtue of the back flow device. xe2x80x9cBack flowxe2x80x9d means the following. The back flow device is being operated in response to a pressure which the first molten resin in the first resin-flow-passage exerts on the second molten resin in the second resin-flow-passage, so that the first molten resin in the first resin-flow-passage flows into the second resin-flow-passage, and as a result, the second molten resin flows toward the second injection cylinder.
In the method of injection molding a multilayered article according to the first aspect of the present invention, when the first molten resin in the first resin-flow-passage is allowed to flow into the second resin-flow-passage on the basis of operation of the back flow device after completion of injection of the first molten resin, specifically, a dwell pressure is applied with the first injection cylinder, and after the completion of injection of the first molten resin, the back flow device is operated to allow the first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage (see FIG. 16). Further, when the first molten resin in the first resin-flow-passage begins to flow into the second resin-flow-passage on the basis of operation of the back flow device during the injection of the first molten resin, the inflow of the first molten resin into the second resin-flow-passage may be completed during the injection of the first molten resin (see FIG. 14), concurrently with the completion of injection of the first molten resin or during the application of a dwell pressure after completion of injection of the first molten resin (see FIG. 15).
A method of injecting molding a multi-layered article, according to a second aspect of the present invention for achieving the above object, is a simultaneous-injection molding method for which the above injection molding apparatus of the present invention is applied. That is, the method of injection molding a multi-layered article, according to the second aspect of the present invention for achieving the above object, is a method using an injection molding apparatus which comprises;
(a) a mold having a cavity block provided with a cavity and a hot runner block,
(b) at least a first injection cylinder and a second injection cylinder,
(c) a first resin-flow-passage for connecting an inside of the first injection cylinder and the cavity, and
(d) a second resin-flow-passage for connecting an inside of the second injection cylinder and the cavity,
the injection molding apparatus having a structure in which;
those portions of the first and second resin flow-passages which are located within the mold are provided in the hot runner block, and
the first resin-flow-passage and the second resin-flow-passage meet with each other in a junction portion upstream of a gate portion opened to the cavity,
the injection molding apparatus being provided with back flow device for letting first molten resin in the first resin-flow-passage flow into the second resin flow-passage after second molten resin is injected into the cavity through the second resin-flow-passage,
the back flow device being operable in response to a pressure which the first molten resin in the first resin-flow-passage exerts on the second molten resin in the second resin-flow-passage,
the method comprising the steps of;
(A) injecting first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage,
(B) injecting second molten resin prepared in the second injection cylinder into the cavity through the second resin-flow-passage during the injection of the first molten resin, and
(C) after completion of injection of the second molten resin, letting first molten resin in the first resin-flow-passage flow into the second resin-flow-passage on the basis of operation of the back flow device during the injection of the first molten resin or after completion of injection of the first molten resin.
FIGS. 17, 18 and 19 show changes of injection pressure, etc., with the lapse of time in the method of injection molding a multi-layered article according to the second aspect of the present invention. When the first molten resin in the first resin-flow-passage is allowed to flow into the second resin-flow-passage on the basis of operation of the back flow device after the completion of injection of the first molten resin, specifically, a dwell pressure is applied with the first injection cylinder, and after completion of injection of the first molten resin, the back flow device is operated to allow the first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage (see FIG. 19). Further, when the first molten resin in the first resin-flow-passage begins to flow into the second resin flow-passage on the basis of operation of the back flow device during the injection of the first molten resin, the inflow of the first molten resin into the second resin-flow-passage may be completed during the injection of the first molten resin (see FIG. 17), concurrently with completion of injection of the first molten resin or during the application of a dwell pressure after completion of injection of the first molten resin (see FIG. 18).
In the method of injection molding a multi-layered article according to the second aspect of the present invention, preferably, in the step (B), the injection amount of the first molten resin per unit time is greater than the injection amount of the second molten resin per unit time. Although depending upon injection molding conditions, a main portion of the multi-layered article may be formed to have a three-layer structure of the first resin layer/the second resin layer/the first resin layer. Otherwise, part of a main portion of the multi-layered article may be formed to have a three-layer structure of the first resin layer/the second resin layer/the first resin layer. In these cases, a portion other than the main portion of the multi-layered article is formed of a layer of the first resin.
The method of injection molding a multi-layered article, according to a third aspect of the present invention for achieving the above object, is an injection molding method for which the above injection molding apparatus of the present invention is applied, the method comprising the steps of;
(A) injecting first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage and then terminating the injection of the first molten resin, (B)
injecting second molten resin prepared in the second injection cylinder into the cavity through the second resin-flow-passage and then terminating the injection of the second molten resin, and
(C) applying a dwell pressure with the first injection cylinder and letting first molten resin in the first resin-flow-passage flow into the second resin-flow-passage on the basis of operation of the back flow device.
FIG. 20 shows changes of injection pressure, etc., with the lapse of time in the method of injection molding a multi-layered article according to the third aspect of the present invention.
The method of injection molding a multi-layered article, according to a fourth aspect of the present invention for achieving the above object, is an injection molding method for which the above injection molding apparatus of the present invention is applied, the method comprising the steps of;
(A) injecting first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage,
(B) injecting second molten resin prepared in the second injection cylinder into the cavity through the second resin-flow-passage during the injection of the first molten resin,
(C) terminating the injection of the first molten resin and the injection of the second molten resin almost at the same time, then, applying a dwell pressure with the first injection cylinder, and letting first molten resin in the first resin-flow-passage flow into the second resin-flow-passage on the basis of operation of the back flow device.
FIG. 21 shows changes of injection pressure, etc., with the lapse of time in the method of injection molding a multi-layered article according to the fourth aspect of the present invention.
In the injection molding apparatus for injection molding a multi-layered article according to the present invention, or in the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, preferably, the back flow device (counter-flow device) allows a constant amount of the first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage. Preferably, further, when second molten resin is being injected into the cavity through the second resin-flow-passage and after the injection of the second molten resin is completed, the inside of the second injection cylinder and the cavity are brought into a communicated state by virtue of the back flow device, and after a predetermined amount of the first molten resin in the first resin-flow-passage is allowed to flow into the second resin-flow-passage, the inside of the second injection cylinder and the cavity are brought into a non-communicated state on the basis of operation of the back flow device. xe2x80x9cPredetermined amountxe2x80x9d and xe2x80x9cconstant amountxe2x80x9d have a relationship of (predetermined amount)xe2x89xa6(constant amount). Alternatively, preferably, when second molten resin is being injected into the cavity through the second resin-flow-passage and after the injection of the second molten resin is completed, the inside of the second injection cylinder and the cavity are brought into a communicated state by virtue of the back flow device, and after the first molten resin in the first resin-flow-passage begins to flow into the second resin-flow-passage, the inside of the second injection cylinder and the cavity are brought into a non-communicated state on the basis of operation of the back flow device.
In the injection molding apparatus for injection molding a multi-layered article according to the present invention, or in the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, preferably, the back flow device is provided in that part of the second resin-flow-passage which is between the junction portion of the first and second resin-flow passages and the second injection cylinder. In this case, particularly preferably, the back flow device is provided between the nozzle portion of the second injection cylinder and the mold, or in the nozzle portion of the second injection cylinder.
In the injection molding apparatus for injection molding a multi-layered article according to the present invention, or in the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, preferably, the back flow device is a back flow control valve (a counter-flow control valve) from the viewpoint of allowing a constant amount of the first molten resin to flow into the second resin-flow-passage and from the viewpoint of structural simplification. The back flow control valve includes a ball-type back flow control valve and a sliding valve-type back flow control valve.
In the injection molding apparatus for injection molding a multi-layered article according to the present invention, or in the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, the volume of the first molten resin which is allowed to flow into the second resin-flow-passage is 5 to 50%, preferably 5 to 35%, more preferably 5 to 25%, based on the cavity volume. When the volume of the first molten resin which is allowed to flow into the second resin-flow-passage is less than 5% based on the cavity volume, it is difficult to prevent the resin which is not to compose the outermost layer of a multi-layered article from coming to exist on the outermost layer surface thereof. Although depending upon injection conditions, the resin layers composing the layers of a multi-layered article undergo turbulence since the first molten resin is allowed to flow into the second resin-flow-passage. For reliably preventing the above turbulence, the volume of the first molten resin which is allowed to flow into the second resin-flow-passage is preferably 35% or less, particularly preferably, 25% or less, based on the cavity volume. When the above amount of the first molten resin exceeds 50% based on the cavity volume, the resin layers composing the layers of a multi-layered article may have a turbulence which is a practical problem in many cases.
In the injection molding apparatus for injection molding a multi-layered article according to the present invention, or in the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, the multi-layered article may have any structure or form, and it includes a parison as a precursor for forming a multi-layered container (multi-layered bottle). In this case, the outermost layer of the parison is preferably formed of the first molten resin injected into the cavity through the first resin-flow-passage. Further, in addition to the parison, the multi-layered article includes a bumper and a steering wheel for an automobile. Further, the multi-layered article also includes a multi-layered article formed by combining a plurality of resins for imparting it with different functions such as strength, an appearance and the like, on the basis of a multi-layer forming technique.
In the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, the second resin is at least one resin selected from the group consisting of a thermoplastic resin having gas barrier properties (gas-barrier resin), a recycled polyethylene terephthalate resin (including a polyethylene terephthalate resin reclaimed from a resin once used in the production of parisons) and a colored polyethylene terephthalate resin.
The above gas-barrier resin is preferably at least one resin selected from the group consisting of a m-xylylene-group-containing polyamide resin (MX nylon resin), a saponification product of an ethylene-vinyl acetate copolymer resin, a polyacrylonitrile resin and a polyvinylidene chloride resin. Of these resins, MX nylon resin is particularly preferred.
The above MX nylon resin refers to a polymer containing at least 70% of structural units obtained from m-xylylenediamine alone, or a xylylenediamine mixture of m-xylylenediamine with 30% or less of p-xylylenediamine, and an a o-aliphatic dicarboxylic acid having 6 to 10 carbon atoms. Examples of the above polymer include homopolymers such as poly-m-xylyleneadipamide, poly-m-xylylenesebacamide and poly-m-xylylenesuberamide; copolymers such as a m-xylylene/p-xylyleneadipamide copolymer and m-xylylene/p-xylylenesuberamide copolymer; and copolymers obtained from the above hompolymer or copolymer components and aliphatic daimines such as hexamethylenediamine, alicyclic diamines such as piperazine, aromatic diamines such as p-bis-(2-aminoethyl) benzene, aromatic dicarboxilic acids such as terephthalic acid, lactams such as xcex5-caprolactam, xcfx89-aminocarboxylic acids such as xcfx89-aminoheptanoic acid or aromatic aminocarboxylic acids such as p-aminobenzoic acid. The above polymers may contain polymers such as nylon 6, nylon 6, nylon 610 or nylon 11.
The relative viscosity of the MX nylon resin is properly at least 1.5, preferably 2.0 to 4.0. The relative viscosity (xcex7rel) is a viscosity measured at 25xc2x0 C. under a condition of resin 1 gram/96% sulfuric acid 100 ml.
In the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, the first resin is at least one resin selected from the group consisting of thermoplastic polyester resins such as polyethylene terephthalate and polyethylene-2,6-naphthalate; a thermoplastic copolyester resin; a polyolefin resin; an aliphatic polyamide resin; a polycarbonate resin; a polyacrylonitrile resin; a polyvinyl chloride resin; and a polystyrene resin. Of these, thermoplastic polyester resins are preferred. Further, a blend prepared by blending two or more resins, e.g., a blend prepared by blending a polyethylene terephthalate resin and a polyethylene-2,6-naphthalate resin may be used as required.
The above polyethylene terephthalate refers to a polyester obtained from an acid component containing at least 80 mol %, preferably at least 90 mol %, of terephthalic acid and a glycol component containing at least 80 mol %, preferably at least 90 mol %, of ethylene glycol. The balance of the acid component is selected from isophthalic acid, diphenyl ether-4,4-dicarboxylic acid, naphthalene-1,4, or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane-1,10-decarboxylic acid and hexahydroterephthalic acid. The balance of the glycol component is selected from propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, cyclohexanedimethanol and 2,2-bis(4-hydroxyethoxyphenyl)propane. Further, there may be used a polyester resin containing p-hydroxybenzoic acid as a hydroxy acid.
Further, the polyethylene-2,6-naphthalate may contain other ester-forming units in an amount of 20 mol % or less, preferably 10 mol % or less in addition to ethylene-2,6-naphthalenedicarboxylate. A dicarboxylic acid for forming the xe2x80x9cotherxe2x80x9d ester-forming units preferably includes aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4xe2x80x2-diphenylcarboxylic acid and 3,4xe2x80x2-diphenylcarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid and dodecanedioic acid; and aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, decalindicarboxylic acid and tetralindicarboxylic acid. A diol for forming the xe2x80x9cotherxe2x80x9d ester-forming units preferably includes aliphatic glycols such as propylene glycol, trimethylene glycol, diethylene glycol and 1,4-butanediol; aliphatic glycols such as 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol and 1,6-cyclohexanediol; and aromatic glycols such as bisphenol A. The above polyethylene-2,6-naphthalate may have a molecule whose terminal is blocked with a small amount of a monofunctional compound such as benzoic acid, benzoylbenzoic acid, benzyloxybenzoic acid or methoxypolyethylene glycol. Further, it may contain a small amount of a polyfunctional compound such as glycerin, trimesic acid or pentaerythritol.
The intrinsic viscosity of the above thermoplastic polyester resin is properly at least 0.40, preferably 0.50 to 1.4. When the above intrinsic viscosity is less than 0.40, an obtained multi-layered article (e.g., multi-layered bottle) is poor in mechanical strength, and further, it is difficult to produce, e.g., a multi-layered article in an amorphous and transparent state. The xe2x80x9cintrinsic viscosity (xcex7)xe2x80x9d is a viscosity measured at 30xc2x0 C. using mixed solvents of phenol/tetrachloroethane=6.4 (weight ratio).
The above thermoplastic copolyester resin refers to a copolyester resin obtained by copolymerizing at least one acid component and at least one diol component. The acid component is selected from terephthalic acid, isophthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid. The diol component is selected from ethylene glycol, propylene glycol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,3-bis(2-hydroxyethoxy)benzene, and 1,4-bis(2-hydroxyethoxy)benzene. The above thermoplastic copolymer resin may be used with other thermoplastic polyester resin as required.
In the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, a combination of a thermoplastic polyester resin, particularly, a polyethylene terephthalate resin (PET resin), with MX nylon resin is most preferred, since these resins are excellent in all of transparency, mechanical strength, injection moldability and stretch blow moldability. Further, since these two resins have similar thermal properties, it is easy to determine molding temperature conditions. In this case, preferably, the polyethylene terephthalate resin and the MX nylon resin have melt viscosity values close to each other. For example, when a polyethylene terephthalate resin having an intrinsic viscosity of 0.7 to 0:8 is used, it is desirable to use an MX nylon resin having a relative viscosity of approximately 2.7. When another gas-barrier resin is used, preferably, the gas-barrier resin has a melt viscosity close to the melt viscosity of the polyethylene terephthalate resin.
In the method of injection molding a multi-layered article according to any one of the first to fourth aspects of the present invention, further, the first resin, the second resin or each of resins forming a multi-layered article may contain a colorant, an ultraviolet absorbent, an antistatic agent, an antioxidant, a lubricant, a nucleating agent, a bactericide and a fungicide.
The injection molding apparatus of the present invention is provided with the back flow device for allowing first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage. When first molten resin is injected into the cavity, therefore, first molten resin (which has flowed into the second resin-flow-passage in a previous molding cycle) has been present in that portion of the second resin-flow-passage which is near the junction portion of the resin-flow-passages. Therefore, a phenomenon that first molten resin to be injected is mixed with second molten resin in the second resin-flow-passage in the vicinity of the junction portion can be prevented, and a phenomenon that second molten resin which is not in an injected state is taken into first molten resin which is being injected can be prevented. As a result, there can be reliably prevented a problem that second resin comes to exist on the surface of a multi-layered article.
In the method of injection molding a multilayered article according to any one of the first to fourth aspects of the present invention, the injection molding apparatus of the present invention is used which is provided with the back device for allowing first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage. When first molten resin is injected into the cavity in the step (A), therefore, first molten resin (which has flowed into the second resin-flow-passage in a previous molding cycle) has been present in that portion of the second resin-flow-passage which is near the junction portion of the resin-flow-passages. Therefore, a phenomenon that first molten resin to be injected is mixed with second molten resin in the second resin-flow-passage in the vicinity of the junction portion can be prevented, and a phenomenon that second molten resin which is not in an injected state is taken into first molten resin which is being injected can be prevented. As a result, there can be reliably prevented a problem that second resin comes to exist on the surface of a multi-layered article.
In the present invention, the back flow device constituted of a back flow control valve (a counter-flow control valve) can avoid an increase in the size of an injection molding apparatus and a complication of the apparatus, and prevents the leakage of molten resin from the resin-flow-passages. When a ball-type back flow control value is used as a back flow control valve, nothing but a ball moves under a fluid pressure, the back flow control valve is structurally simple, and neither a movable part nor a sliding part is present. The control of a fluid with a ball-type back flow control valve can be applied not only to the flow of a molten resin but also to the flow of each of a liquid and a gas. When a conventional shut-off valve is used, an electromagnetic valve or cylinder is operated with an external hydraulic pressure or air pressure, and the flow passage of a fluid is forcibly opened and closed with the rotation or reciprocal movement thereof. Therefore, the conventional shut-off valve is structurally complicated and has poor durability.